1. Field of the Invention
This invention relates to an apparatus and a method for manufacturing a golf ball, especially a golf ball having a multilayer structure.
2. Description of the Related Art
There are conventional methods for manufacturing a multilayer golf ball, and three of the methods are shown as follows, for example.
A first method for manufacturing a golf ball comprises the steps of, vulcanization molding an inner core, retaining the inner core at a fixed position with a movable pin, injecting material which composes outer layer by an injection molding machine or a transfer metallic mold, pulling off the movable pin, and vulcanization molding the outer layer.
A second method for manufacturing a golf ball comprises the steps of forming a pair of unvulcanized half outer layer bodies by metallic molds, which consists of a hemispherical concave mold and a hemispherical convex mold (or forming a pair of half outer layer bodies by heating the half outer layer bodies which is unvulcanized for a fixed time so that not to shrink the half outer layer bodies), inserting an inner core vulcanization molded separately into the half outer layer bodies, and vulcanization molding the half outer layer bodies and the inner core.
A third method for manufacturing a golf ball is as set forth in the second method, wherein each of the outer layers are not shaped into hemispherical appearance but shaped in sheet appearance.
However the conventional methods described above are not suitable for manufacturing a golf ball having a multilayer structure.
When manufacturing a golf ball by the first method, a whole structure of the metallic mold apparatus is extremely complicated and a limitation of pressure for injecting material causes decrease of a number of golf balls to be produced per one press and makes the method unsuitable for mass production of golf balls. Furthermore it is difficult to fix a diametrical dimension of a hole portion of a metallic mold for inserting a movable pin. When a clearance between an outer circumferential face of a movable pin and an inner face of a metallic mold hole portion is too small, the movable pin is not able to move smoothly, and if the clearance is too large, rubber is possible to outflow from this clearance.
When manufacturing a golf ball by the second method, the metallic mold is opened after molding a half outer layer body and the adhesion of the half outer layer body either to convex mold or to a concave mold is unpredictable, and the method is impossible to mass-produce golf balls. The third method only differs from the second method for having the sheet appearance half outer layer body, and this method has the same defects as the second method.